Dimensionally stable hydrophilic foam and method of preparing same

ABSTRACT

Resilient, crosslinked, hydrophilic, open-celled polyoxyalkylene urea/urethane foam comprising hydrophilic and hydrophobic segments of relatively high molecular weight, the foams having relatively high resistance to bottoming out and good dimensional stability with absorption of water, and a process for preparing the same.

Utlited States Patent 1 1 Kyle et al. 1 Oct. 1, 1974 [541 DIMENSIONALLY STABLE HYDROPHILIC 3,402,094 9/1968 Levitch 161/159 O AND METHOD OF PREPARING 3,451,885 6/1969 Klein 1 161/159 3,534,852 10/1970 Posner 161/159 SAME Inventors: Robert C. Kyle; John F. Kistner,

both of 3 M Center, Minneapolis, Minn. 55133 Filed: Apr. 9, 1973 Appl. No.: 349,275

Related U.S. Application Data.

Division of Ser. No. 236,465, March 20, 1972, Pat. No. 3,793,241.

U.S. Cl 161/159, 156/148, 161/151, 161/190 Int. Cl B32b 3/26, B32b 5/18 Field of Search 161/159, 151, 190; 156/148 References Cited UNITED STATES PATENTS 5/1968 Willard et al. 161/159 Primary ExaminerWi1liam J. Van Balen Attorney, Agent, or FirmAlexander, Sell, Steldt & DeLaHunt [57] ABSTRACT Resilient, crosslinked, hydrophilic, open-celled polyoxyalkylene urea/urethane foam comprising hydrophilic and hydrophobic segments of relatively high molecular weight, the foams having relatively high resistance to bottoming out and good dimensional stability with absorption of water, and a process for preparing the same.

3 Claims, No Drawings DIMENSIONALLY STABLE HYDROPHILIC FOAM AND METHOD OF PREPARING SAME This is a division, of application Ser. No. 236,465, filed Mar. 20, 1972 now U.S. Pat. No. 3,793,241.

BRIEF SUMMARY OF THE INVENTION The present invention relates to resilient, crosslinked, hydrophilic, open-celled polyoxyalkylene urea- /urethane foam comprising hydrophilic and hydrophobic segments of relatively high molecular weight, the foams having relatively high resistance to bottoming out'and good dimensional stability with absorption of water. The foams are useful in various cushioning applications, particularly in the area of shoe insoles. The invention also relates to a process for the preparation of the foams.

Polyoxyalkylene/polyisocyanate-type polyurethane foams, have been disclosed heretofore, e.g. see U.S. Pat. Nos. 2,949,431, 2,965,584, 3,413,245, 3,021,290 and 3,457,203. These foams are of use as sponges, washcloths, mops, etc. but generally are unsatisfactory in cushioning products designed to bear weight since they do not also combine the properties of density, strength, firmness and resilience in sufficient degree. In some applications also, including that of shoe insoles, the considerable expansion of these foams upon absorption of water cannot be tolerated.

Certain prior art polyurethane foams have been disclosed to be useful as cushions. Such foams,'however, lack the combination of properties of the present materials and would not be satisfactory in their primary areas of use. Thus, U.S. Pat. No. 3,021,290 discloses foams prepared from a polyalkylene ether glycol, an organic polyisocyanate having two to three functional isocyanate groups, an activator mixture comprising a small amount of water (not more than 5 percent of the weight of the glycol and the isocyanate) together with a reaction catalyst and a wood cellulose filler. Considerable heat is required to bring about the foaming reaction to produce the compositions of the aforesaid patent (e.g. 1 hour at 115 to 120 C., room temperature for 16 hours then 1 to 120 C. for an additional 8 hours). The resulting foams are disclosed in the patent to have densities between 2 and 3 pounds per cubic foot, and compress to 50 percent of their initial thick ness under pressures of about 0.8 pound per square inch. These foams differ greatly from the foams of the present invention as to their physical properties as well as their chemical makeup.

Foamed shoe insoles are known but they utilize closed cell, hydrophobic foams. The closed cell structure has been necessary in such compositions to obtain both the needed resistance to bottoming out at high load and the softness at low load, and to achieve them in the necessarily thin cross section of shoe insoles. Such foams, however, can be quite uncomfortable. The closed cell structure (which does not breathe) does not allow the heat generated by the foot to dissipate or the moisture from perspiration to be removed from the surface of the foot. Even had it been possible to develop sufficient load carrying properties with insoles of opencelled foams of the hydrophobic types previously used, there would have been considerable discomfort, since, under high loads, the moisture would be squeezed back out of the foam and into contact with the foot. These problems of heat and moisture, furthermore, become considerably more acute when the wearer is walking,

running, or otherwise exercising, since both are then generated by the foot in considerably greater quantities. The pressure and frequency of flexing are also greater when the wearer is exercising.

It is an object of the invention to provide novel resilient open-celled hydrophilic polyoxyalkylene urea/urethane foams. It is another object of the invention to provide novel unitary articles comprising in combination a resilient opencelled hydrophilic polyoxyalkylene urea/urethane foam portion and a fibrous assembly portion. It is another object of the invention to provide shoe insoles comprising resilient opencelled hydrophilic polyoxyalkylene urea/urethane foam. It is another object of the invention to provide unitary articles comprising in combination resilient open-celled hydrophilic polyoxyalkylene urea/urethane foam and a needle punched fibrous assembly. It is another object of the invention to provide unitary articles comprising in combination resilient opencelled hydrophilic polyoxyalkylene urea/urethane foam and fibrous assembly portions which have been needle punched together. It is a further object of the invention to provide a process for the preparation of resilient open-celled hydrophilic polyoxyalkylene urea/urethane foams. Still other objects of the invention will become apparent to those skilled in the art from reading this specification.

DETAILED DESCRIPTION The foams of the present inventioncomprise in the main an intimate physical intermixture of two polymeric networks which are for the most part chemically separate but which contain a minor proportion of chemical (urea and urethane) links between them, the first network being hydrophilic and the second being hydrophobic. The hydrophilic network contains hydrophilic oxyalkylene chains joined together by urea linkages and, at most, a low degree of crosslinking. The hydrophobic network contains hydrophobic oxyalkylene chains joined through groups of the type Ar(NHCO- wherein Ar is an n-valent aromatic group and n is greater than 2. Preferably n is not more than 4, most preferably it is not greater than 3. The hydrophobic network is more highly crosslinked and serves to reinforce and stabilize the foam (resulting in considerably greater dimensional stability with water absorption and resistance to bottoming out).

Due to the hydrophilic nature of the foams, a considerable amount of the water they absorb under conditions of high humidity (and release under conditions of lower humidity) is bound water which is absorbed by the composition itself and cannot be removed by pressure or wringing out. This is in contrast to hydrophobic foams in which water taken into the void spaces can be all or substantially all removed by pressure.

The hydrophilic and open-celled properties of the foams of the invention, in combinationwith their other properties render them particularly suitable for use in cushion applications in which the foam is used in close proximity to the surface of the human body. Exemplary of such applications is the shoe insole. Shoe insoles are used to obtain resilience, support and comfort for the foot whether the wearer is sitting, standing, walking or running. To provide the necessary resilience and support, the composition must, in a relatively thin cross section, resist bottoming out," i.e., reaching an essentially uncompressible state, even under relatively high pressures. At the same time it is desirable that the insole be relatively soft under low pressures, i.e., have relatively high deflection at low load. Insoles should also spring back to nearly full thickness after repeated or prolonged compressions under the conditions of use, i.e., have low compression set.

More specifically, the present invention relates to resilient, crosslinked, hydrophilic, open-celled polyoxyalkylene urea/urethane foam comprising two types of relatively high molecular weight segments as follows:

A. hydrophilic segments containing polyoxyalkylene chains predominently interconnected by urea links, at least 50 percent of the individual oxyalkylene groups therein being oxyethylene groups, and

B. hydrophobic segments containing polyoxyalkylene chains and aromatic hydrocarbon groups predominently interconnected by urethane links, the individual oxyalkylene groups substantially all containing more than two carbon atoms, the foam having 1. A water absorbing capacity (AW of at least about 700 percent by weight.

2. A density of at least 8 pounds per cubic foot (125 kg/m).

3. A volume change upon absorption of water (AV ,/AW,,) of less than 0.4 percent per weight percent of absorbed water.

4. A 24 hour compression set (AC) of less than 75 percent.

5. A bound water pickup (AWh) of at least 100 percent by weight. Ordinarily and preferably, the volume change of the foam with water absorption, AV is not more than about 35 percent in the foams of the invention. Test procedures for measuring these properties are described hereinafter.

The foams of the invention may be cast in molds or spread as films. The surface of such foams has a tough skin which, nevertheless, has the same moisture absorptivity the body of the foam because the polymer itself is hydrophilic. The skin is such that cushions and pads molded from the foam form stable, tear-resistant and smooth surfaces and, therefore, for many purposes advantageously do not require a protective fabric or coating. Because of the resilience, compression set re sistivity, softness, moisture absorption and water vapor transmission properties of the foams, highly desirable and comfortable cushions and pads for use in contact with the human body may be prepared, as, for example, cushions for chairs, farm equipment, sofas, automobiles and other vehicles and pads for protection of various parts of the anatomy such as protective pads for athletes, e.g. knee pads, kidney pads, shoulder pads and helmet liners. Sweat bands for use in hats, and head coverings per se are also contemplated, as are pads for underarm protection of clothing.

As previously noted, an especially valuable use of the stucturally reinforced hydrophilic foams of the invention is in insoles for shoes and boots. The foam provides a satisfactory supporting foundation for the foot and is equal to or better than leather in its softness, moisture absorption and moistureand air-permeability. Insoles may be cut to shoe sole shape from a sheet of the foam that has been cast to one-eighth inch or more in thickness (preferably about one-fourth inch) and that has a tough surface skin. The upper and/or lower surface of the insole may have one or more layers of a woven or non-woven f ber textile material fastened to it.

' crimped continuous fibers which, when coated and im- I A wide variety of fibrous assemblies (including woven and non-woven fabrics, compressible mats, etc.) can be used in connection with the foamed compositions of the present invention. These can be adhered to one or both sides of already formed foam (e.g. using a spray adhesive), or the foam can be formed in contact with a fibrous assembly, or between two assemblies, or the assembly can be impregnated with the liquid foamforming composition and the latter then foamed. Such fibrous assemblies impart desirable properties to the overall composite such as improved tensile properties, increased dimensional stability and surface toughness and strength. Normally the fibrous assemblies are breathable, in order to take advantage of the hydrophilic nature of the underlying foam.

If desired, a fibrous assembly can be compressed or molded during or just after foaming, or prior to combining with the foamed composition, and correspond ingly a wide variety of products can be obtained. The assembly of fibers can be a mat of interpenetrated pregnated with the compositions of the invention, form a leather-like sheet material. Another satisfactory fibrous assembly is non-woven nylon fabric such as, for example, nylon scrim.

Another embodiment of shoe and boot insoles prepared from the structurally reinforced hydrophilic foams of the invention comprises a layer of the reinforced hydrophilic polyoxyalkylene foam that has been made by skiving large loaves of the foam into sheets having a thickness of from about 0.12 to 0.5 inches. (This skived foam can also be used in other cushion and pad applications such as those described above.) One or more layers of a textile fabric or polymer film may be fastened to the sheet of skived foam. A preferred method is to cover a skived foam sheet with a non-woven web of natural or synthetic fibers. This may be done by forming a non-woven web of fibers, such as, for example, a non-woven web from one inch staple 4 denier dacron fibers or nylon fibers in a Rando- Webbcr" machine, superimposing the non-woven web onto the skived foam sheet, and subjecting the assembly to needle punching in a needle felting machine.

In another preferred embodiment, the fibrous assembly is passed through a needle punching machine to effect consolidation of the assembly. The punched assembly' is then impregnated with the liquid foam forming composition of the invention. Alternatively, the foam can be prepared separately and a fiber assembly, such as a randon webbed material of rayon, nylon, etc., needle punched directly onto (and through) the foam using 30-50 punches per square inch, with or without an adhesive. The fibrous assemblies in these embodiments provide a pleasant feel and additional resistance to swelling of the foam upon absorption of moisture.

The needle punching forces fibers of the web into and through the foam to lock the web to the foam and also to provide a covering of fibers on the reverse side of the foam. The sheets of hydrophilic foam having a covering of non-woven fibers bonded by needle punching may then be cut to size to form dimensionally stable insoles.

The Rando-Webber machine for making the nonwoven web is available from the Curlator Corporation of East Rochester, New York. Needle punch machines suitable for bonding non-woven webs to various substrates are available from the James Hunter Corporation of North Adams, Massachusetts.

The sheets of hydrophilic foam having a covering of non-woven fibers bonded by needle punching may also be used in clothing, eg for linings of arctic clothing where the hydrophilic foam provides insulation and comfort because of its capacity to absorb water vapor and lose moisture by transpiration.

The foams of the present invention are prepared by l. Forming-a miscible blend of 100 parts of a water soluble linear hydrophilic isocyanateterminated polyoxyalkylene prepolymer (I) having a molecular weight of from about 400 to 3000 and in which at least 50 percent of the oxyalkylene groups are oxyethylene and from 3 to parts of an aromatic isocyanate compound '(II) having an isocyanate functionality greater than 2 and an equivalent weight with respect to isocyanate of from about 80 to 240.

2. Dispersing to 60 parts of a linear hydrophobic hydroxyl-terminated polyalkylenc oxide prepolymer (Ill) having a molecular weight of about 400 to 6000 in at least 20 parts of water.

3. Mixing the blend of step (I with the dispersion of step (2) at a temperature at which the dispersion is liquid. but not above 10 C. to form a homogeneous mixture, and

4. Maintaining the mixture at a temperature below C. until the resulting chemical reaction is substantially complete and a solid foam has been formed.

The weight ratio of the water to the total weight of the other three components in the charge may be 2 or more and is preferably 0.5 to l.5. If desired. fillers. surfactants, colorants, reaction catalysts. etc. can be added to blend l or dispersion (2) before the two are mixed.

The four constituents of the process and the reactive species in each are as follows:

In blend (1) I The hydrophilic prepolymer NCO groups II The polyfunctional aromatic NCO groups isocyanate in dispersion 12) Ill The hydrophobic prepolymer OH groups I\' The water H- Neither blend l nor dispersion (2) reacts chemically. However. when the two are combined to form the foaming mixture. chain extending and crosslinking reactions take place simultaneously and rapidly. The speed of reaction will vary somewhat depending upon the particular materials present. and the concentrations thereof but generally 'if the constituents are at room temperature (about 25 C.) when combined. the mixture must be coated. cast or molded within 1 minute. If the dispersion is cooled to ice temperature (about 0 C.) the time can be extended to 2 to 3 minutes. or in some cases to as long as 10 minutes. The foam forms and solidifies quickly (usually within 45 minutes at room temperature). Within 2 hours at room temperature the reaction is substantially complete and the foam has reached its final properties and can be used. Any excess of water present can be removed simply by squeezing the foam or air drying.

Formation of a molecule of gas and a urea group T NCO H 0 NHCOOII NH COgl isocyanate earbamie acid immediate amine gas (unstable decomposition 0 H l) H NH: NCO NCN amine isocyanate urea Formation of a urethane group 11 II N C O H O M N C O M isocyanate hydroxyl urethane The individual chemical reactions occurring in the foam formation can be characterized as follows:

Of these possible reactions. the reaction of the isocyanate groups of prepolymer I with the water IV (resulting in long chain, hydrophilic, essentially linear segments consisting essentially of oxyalkylene chains joined by urea groups) and'the reaction of the isocyanate groups of polyfunctional aromatic isocyanate compound II with the hydroxyl groups of prepolymer Ill (resulting in relatively high molecular weight. hydrophobic crosslinked segments consisting essentially of oxyalkylene chains joined by groups of the type Ar(NHCO- wherein Ar is an n-valent aromatic group and n has an average value greater than two) are strongly favored. The tendency of I to react with IV rather than with III is shown by its relative reaction rates with them. i.e. l reacts in minutes (eg. 3-5 minutes) with IV but requires hours (e.g. 8-24 hours) to react with III. Compound II and prepolymer III are both water insoluble. but II is soluble in III. Also [I reacts with water more slowly than does 1. Thus. the reaction of II with III is also favored.

The linear. or essentially linear. segments formed by the reaction of I with IV provide the hydrophilic properties of the present foams and the crosslinked segments formed by the reaction of II with III provide additional stiffening. resilience. compression setresistance and reduced expansion with absorption of water. The greater the proportion of compound II used compared to prepolymer I. the smaller is the expansion of the foam obtained and the lower is the water pickup of the foam.

In spite of the favored reactions, an occasional isocyanate group ofI will react with an hydroxyl group of III and an occasional isocyanate group of II will react with water and the resulting amine function with an isocyanate group of I. These occasional reactions between the two types of segments combine them into a single. uniform permanent network.

The large stoichiometric excess of water present (with respect to all of the isocyanate groups charged) insures that all of the isocyanate groups will be consumed in the reaction. In addition, the water acts as a heat sink to maintain the reaction temperature below 25 C. This is helpful since the reaction temperature is normally maintained below 25 C. (and preferably from 0 to 10 C.) to ensure development of the density and strength characteristics of the compositions. It has been found that if the temperature is allowed to rise to higher temperatures. the resulting foam is much less dense and has larger pores.

Upon mixing constituents I. II. III and IV (and. if desired. additives of the types mentioned elsewhere herein) the mass is immediately cast into its desired final shape. e.g. molded or coated a sheet. Thus.

upon mixing, it can be knife coated onto a moving web having a release surface (such as polyethylene coated paper) to foam. The foamed material can be either allowed to set and crosslink with the top surface free or it can be levelled and given a predetermined thickness by passing it through a metering gap. At that time a second web with a release surface can, if desired. be applied to the top surface of the foam. The release web or webs can be removed as soon as the foam has finished reacting and crosslinking or can be left in place for storage.

Methods of preparing hydrophilic prepolymer precursors l of the general type used in the present invention are disclosed in the art. See for example US. Pat. Nos. 2,726,219 and 2,948,69l and Polyurethanes: Chemistry and Technology, by Saunders and Frisch, Part I, lnterscienee Publishers, New York i962). Pre polymers of this type suitable for use in the present invention are generally those in which at least half of the repeating alkylene oxide groups are ethylene oxide groups, with the remainder being other alkylene oxide groups, such as propylene oxide and butylene oxide groups.

Ordinarily the prepolymers are prepared by reacting a polyoxyalkylene polyol with a polyisocyanate using a NCO/OH equivalent ratio of at least 2/1 or slightly higher, e.g. 21/1 to 25/1.

Broadly speaking, the polyoxyalkylene polyols suitable for preparing the hydrophilic prepolymers are water soluble and have molecular weights of at least 300 and as high as 7000 (preferably between about 600 and 2000). The most preferred polyols are polyoxyethylene diols having molecular weights between about 600 and 1500.

Generally the higher the molecular weight of the polyol the tougher and denser are the foams prepared therefrom. Also, the higher the ratio of oxypropylene or other oxyalkylene units to oxyethylene units in those polyols, the greater is the resistance to compression set and the lower is the moisture absorption capacity ofthe foams prepared therefrom.

Commercially available polyols suitable for use in preparing the prepolymers l are: oxyethyleneoxypropylene block copolymer polyols available (from the Wyandotte Chemicals Corporation) under the trade designation Pluronic," e.g. Pluronic L35," *F38" and P46;" hydrophilic oxyethyleneoxypropylene random copolymer polyols available commercially (from Jefferson Chemical Co.) under the trade designations Polyol Functional Fluids" WL 260 and WL 580; and polyethylene glycols available (from the Union Carbide Corporation) under the trade designation Carbowax," e.g. Carbowax" 600." 1000", 1540" and 4000.

A particularly preferred prepolymer for use in the present invention is the reaction product of 1 mole of polyethylene glycol 1000 (containing approximately 23 repeating ethylene oxide units) with 2 moles of toluene diisocyanate. In this prepolymer and in other similar prepolymers prepared by reactions between diols and diisocyanates, 2 urethane linkages are formed.

Among the polyfunctional aromatic isocyanate compounds II are compounds of the type R'(NCO),,, above. They include, for example, mphenylene diisocyanate, mixtures of toluene-2,4-diisoeyanate and toluene-2,6- diisocyanate, diphenyl-3,3 -dimethyl-4,4- diisocyanates, diphenyl-3,3-dimethoxy-4,4'-

diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylmethane-4,4'-diisocyanate, diphenylmethane- 4,4'-dimethyl-3,3'-diisocyanate, 1,5-naphthalene diisocyanate and aromatic polyisocyanates, e.g. poly(methylenephenylene isocyanates) containing an average of from about 2 to 2.8 isoeyanate groups per molecule. Such poly(methylenephenylene isocyanates) are commercially available under the trade designations Mondur MRS from Mobay Co., Isonate 901 from Upjohn Co. Papi" from the Upjohn Co., etc. Preferred compounds for this use are Mondur MRS and a mixture of percent toluene-2,4-diisocyanate and 20 percent toluene-2,6-diisocyanate.

Among the prepolymers Ill are polyalkyleneoxide polyols such as the polypropyleneoxide polyols available from Union Carbide Company under the trade designation Niax," from Jefferson Chemical Co. under the trade designation Thanol, and from Mobay Chemical Co. under the trade designation Multron." Also useful as the hydrophobic prepolymers III are the polyester polyols such as those available from Wyandotte Co. under the trade name Pluracol, from the Mobay Chemical Co. under the trade names Multrathane R-l4, R-26 and R-l44, and from the Hooker Chemical Co. under the trade name Rucoflex Polyester Polyols."

Other materials which may be incorporated into the hydrophilic foamed compositions of the invention may also include additives such as catalysts, surfactants (to aid in mixing the components of the foam), pigments (to provide color), fibers such as nylon, rayon, etc. preferably cut into short pieces of the order of 0.5 inch or less, and mineral fillers such as finely divided calcium carbonate, tale, mica, etc. In addition, medicaments (to provide therapeutic character to the foams), plasticizers, anti-oxidants and perfumes may be added. Absorbent charcoal can also be employed.

A particularly useful additive is elastomeric particles such as ground tire stock, or other dense elastomerie materials (whether of scrap or virgin stock). Preferably, such particles are of a size that they will just pass through a No. 16 US. Standard Sieve (openings 0.047 inch) although larger or smaller particles can also be used.

Although the hydrophilic foams of the invention can be prepared without a catalyst, it is often advantageous to use a catalyst to promote the formation of urethane and urea bonds. Appropriate catalysts include, but are not limited to, N-methyl morpholine, N-hydroxyethyl morpholine and triethylene diamine. Typical metallic salt catalysts include, for example, the salts of antimony, tin, iron, lead and mercury, e.g., dibutyltin dilaurate, stannous octoate, phenyl mercuric acetate and the like. Broadly speaking. the catalyst is employed in an amount ranging from about 0.05 to about 1.0, and preferably from about 0.1 to about 0.4 percent, by weight of the prepolymer l.

Suitable surfactants are known to the art and include polyoxyethylene derivatives of alkyl and aryl hydroxy and carboxy compounds and sulfonated alkyl and aryl compounds, fatty acid soaps, e.g. calcium octoate, and fluorocarbon surfactants.

The following are test procedures used in characterizing and defining the products of the invention. Water absorbing capacity The water absorbing capacity (or free water pickup) AW is determined by weighing a sample of foam previously dried to constant weight at 25 C. and 50 percent relative humidity (W completely saturating it with water by squeezing the foam under water at about 25 C. until the air is expelled, and holding it under water with weights for minutes. The water-saturated foam is then removed from the water using a tared metal hook and allowed to hang until excess surface water has dripped off. The saturated sample is immediately weighed (W and the free water pickup is calculated using the formula where AW is the free water pickup measured as percent weight gain. It is a measure of the total amount of water that may be held by the foam and includes both the water held mechanically in the open pores of the foam and the water absorbed into the cell walls of the foam. Density The density, in pounds per cubic foot is determined using foam previously dried to constant weight at C. and 50 percent relative humidity. Bound water pickup Bound water pickup is determined by compressing the water saturated sample from the determination of the water absorbing capacity until no more water can be forcibly expelled from the sample. The sample is then weighed (W and the bound water pickup AW,, calculated using the formula where W is as previously defined and W is the bound water pickup measured as percent weight gain. It is a measure of the water absorbed into the cell walls of the foam. 1 Volume change with water absorption The volume change with water absorption is measured in percent per weight percent of bound absorbed water. i.e..

AV /AW The method of determining AW,, has already been given. AV is calculated using the formula where V. is the volume of the dry sample (dried toconstant weight at 25 C. and 50 percent relative humidity) and V. is the volume of the sample after soaking in water and expelling the free water as in the bound water pickup procedure. Twenty-four hour compression set The 24-hour compression set. AC. is expressed as a percentage and is calculated from the formula AC T T /T X 100 where T, is initial foam thickness. T is the thickness of the foam after it has been subjected to a force of 15 pounds per square inch for. '24 hours and allowed to relax (free of the force) for 1 hour. The foam is maintained under ambient conditions (approximately 25 C. and 50 percent relative humidity) throughout this test.

The following examples more specifically illustrate the compositions of the invention and the process for their preparation, but are in no way limiting of the scope thereof. The particular constituents used in the examples are representative of the types which they exemplify but could as well be other constituents of the same classes. The percentages and parts in the examples and elsewhere herein are by weight unless otherwise stated.

Example 1 The constituents used were as follows:

1. Polyethylene glycol having a molecular weight of 1000 end capped with toluene diisocyanate and having the formula OCN ll. Poly(methylenephenylene isocyanate) having a molecular weight of 380, an isocyanate equivalent weight of 135 (thus containing about 2.8 isocyanate groups per molecule) and availableunder the trade designation Mondur MRS" from Mobay Co.

111. Polyoxypropylene diol having a molecular weight of 2000.

Surface active agent. A polyoxyethylene derivative of fatty acid partial esters of hexitol anhydrides available commercially from the Atlas Powder Company under the trade designation "Tween 80".

Into a suitable vessel provided with a stirrer were charged 100 parts of l, 13 parts of 11 and 1 part of the surface active agent. The mixture was stirred until thoroughly blended. In another vessel 32 parts of ill and 100 parts of ice water (about 75 parts ice to 25 parts water) were blended. To this was added the above isocyanate mixture and the resulting mass was stirred thoroughly to produce a homogeneous liquid which was poured into a suitable mold allowing for 5 10 fold expansion. Within minutes the mixture began to foam absorbed water, and a 24 hour compression set of 67 percent.

Example 2 The constituents were as follows: 1. Polyethylene glycol having a molecular weight of 1000 endcapped with a mixture of percent toluene- 2,4-diisocyanate and 20 percent toluene-2,6- diisocyanate.

ll. Poly(methylenephenylene isocyanate) as in Example l.

45.15 parts bentunlte 0.40 parts t-butyl phenol (mold inhibitor preservative) (1.30 parts calcium octoatc 0.45 parts phenyl mercuric acetate Wparts total to prepare a polyol masterbatch.

Into a suitable vessel provided with a stirrer were charged 100 parts of I, parts of 11 and 1 part of the fluorochemical surface active agent. The mixture was stirred until thoroughly blended. In another vessel 45 parts of the polyol masterbatch and 100 parts of ice water (75 parts ice and 25 parts water) were stirred until homogeneous. The polyol-ice water mixture was then added to the isocyanate mixture and thoroughly blended for about 1 to 3 minutes to produce a homogeneous liquid which was poured into a suitable mold to allow for a 5 to fold expansion. Within minutes the mixture began to foam and within 45 minutes at about C. was completely cured.

The nearly white foam was soft and resilient. it had tough smooth surfaces at the air and mold interfaces and was readily slit and skived by automatic equipment. A sample of the foam was found to have a density ofabout 10 lbs/cu. ft., AW,of7 10 percent, AW,, of 150 percent, AV, of 25 percent, AV,./AW,, of 0.17 a 24 hour compression set of 62 percent and a tensile strength of psi.

To illustrate foams prepared without the structurally reinforcing agent of the invention, Example 2 was repeated without adding the polyalkylene polyols (Ill). The properties of this control foam and those of the foam ofthe invention are compared in the following table:

Thus, the foam of the invention is approximately half as dense and 8-9 times more dimensionally stable (with respect to moisture content) than the control foam.

Example 3 lnto a suitable vessel provided with a stirrer were charged 100 parts of l, 10 parts of 11 and 1 part of surface active agent, all as defined in Example 1. Into another stirred vessel 100 parts of the polyol masterbatch of Example 2 and 100 parts of ice water were charged. Both mixtures were separately blended then mixed together until thoroughly blended (approximately 2 minutes) and then immediately poured into a suitable mold.

A sample of the dried foam was found to have a density of 12.3 lb/cu. ft., AW,- of 700 percent, AW of 110 percent, AV, of 21 percent, AV ,./AW,, of 0.20 and a 24 hour compression set of 61 percent.

Example 4 lnto a suitable vessel provided with a stirrerwere charged 100 parts of a hydrophilic isocyanateterminated prepolymer (l) (a polyoxyethylenediol having a molecular weight of 1540 endcapped with toluene diisocyanate, the total molecular weight being 1888), 5 parts of poly(methylenephenylene isocyanate) and 2 parts of surface active agent, the latter two constituents being as in Example 1. In another vessel 45 parts of the polyol masterbatch of Example 2 and 100 parts of ice water were blended. The two were combined and thoroughly mixed after which they were poured into a mold.

A sample of the resulting foam had a density of l 1.8 lb./cu. ft., AW, of 880 percent, AW,, of 260 percent, AV,- of 33.5 percent, AV ,./AW,, of 0.13 and a 24 hour compression set of percent.

Example 5 The cured foam of Example 2 was skived into sheets one-fourth inch thick and subjected to needle punching to attach a rando-web batt thereto. The rando-web consisted of 3 denier rayon fibers approximately l-9/ l 6 inches in length. It was about 1 inch in thickness and had a density of 1.6 pounds per cubic foot prior to needle punching. The needle punching was accomplished using 1 inch strokes, 50 to needles per square inch, and 300 strokes per minute. The rando-web was compressed to about one-eighth inch in thickness in the combined material. The measured properties of the combined material were as follows: tensile strength 60 psi, 24 hour compression set (AC) 50 percent, density 11.5 lbs/ft, AW 700 percent, AW 150 percent, AV,- 15 percent, AV,./AW,, 0.19.

What is claimed is:

1. A unitary article comprising in combination a resilient, crosslinked, hydrophilic, open-celled polyoxyalkylene urea/urethane foam portion comprising two types of relatively high molecular weight segments as follows:

A. hydrophilic segments containing polyoxyalkylene chains prcdominently interconnected by urea links, at least 50 percent of the individual oxyalkylene groups therein being oxyethylene groups, and

B. hydrophobic segments containing polyoxyalkylene chains and aromatic hydrocarbon groups predominently interconnected by urethane links, the individual oxyalkylene groups substantially all containing more than two carbon atoms,

the foam having 1. A water absorbing capacity of at least about 700 percent by weight.

2. A density of at least 8 pounds per cubic foot (125 kg/m).

3. A volume change upon absorption of water of less than 0.4 percent per weight percent of absorbed water.

4. A 24 hour compression set of less than 75 percent.

5. A bound water pickup of at least about percent by weight,

and, integrally joined thereto, a fibrous assembly portron.

2. A unitary article according to claim 1 wherein the fibrous assembly portion is a needle punched nonwoven web.

3. A unitary article according to claim 2 wherein the foam and fibrous assembly portions are joined by needle punching.

v UNITED STATES PATENT omen CERTIFICATE OF CORRECTION PAGE 1 P t n N 2.829.128 bated October 1. low

Robert CQ Kvle and John F. Kistner It is.certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On'page 1 Section [76], "Inventors't Robert C. Kyle John F.

Kistner, both of 3M Center, Minneapolis, Minn. 55l33"-- should be --Inventors: Robert C. Kyle, Minneapolis, and John F. Kistner, Afton, -Minn. assignors to Minnesota Mining; & Manufacturing Company, St. Paul, Minnesota-- Column 5 line --physical-- should be inserted after "final" Column 6, lin'es lfbg "Formation 'of a" molecule of gas and ai urea; group NCO +HO'-- NHCOOH elm-q co isocyanate carbamic acid immediate am ne ga (unstable decomposition NH I NCOm- NCN/vw amine isocyanate urea Formation" of a urethane group H9 NCO HOmv--- NCOn/w isooyanate hydroxyl urethane should be FORM PC3-1050 HO-69) UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 'PAGE '2 Patent Nou 3.839.138 D te October .1. 197

Inventor(s) Robert C. Kvle and John F. Kistner It; is certified thaterror appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

--Formation of a molecule of gas and a urea grog;

MNco u o-wwnncoon ewbm co isocyanate v c'arbamic acid immediate amine ga (unstable) 7 decomposition NH NCO/\,/\+-- MNCNM ami e isocyanate I urea Formation of a urethane groug O H" MNCO HON---- .wNCOW isocyanate hydroxyl urethane Signed and sealed this 17th day of December 1974.

SEAT.)

ttest Z'I'CCOYH GXBSUN JR. C. MARSHALL DATE-5N Attesting Officer Commissioner of Patents FORM P0-1050 (10-69) T uscoMM-DC GOING-P69 n u. s. GOVEINIINT mamas omc: nu o-asc-au. 

1. A UNITARY ARTICLE COMPRISING IN COMBINATION A RESILIENT, CROSSLINKED, HYDROPHILIC, OPEN-CELLED POLYOXYALKYLENE UREA/URETHANE FOAM PORTION COMPRISING TWO TYPES OF RELATIVELY HIGH MOLECULAR WEIGHT SEGMENTS AS FOLLOWS: A. HYDROPHILLIC SEGMENTS, CONTAINING POLYOXYALKYLENE CHAINS PREDOMINENTLY INTERCONNECTED BY UREA LINKS, AT LEAST 50 PERCENT OF THE INDIVIDUAL OXYALKYLENE GROUPS THEREIN BEING OXYETHYLENE GROUPS, AND B. HYDROPHOBIC SEGMENTS CONTAINING POLYOXYALKYLENE CHAINS AND AROMATIC HYDROCARBON GROUPS PREDOMINENTLY INTERCONNECTED BY URETHANE LINKS, THE INDIVIDUAL OXYALKYLENE GROUPS SUBSTANTIALLY AL CONTAINING MORE THAN TWO CARBON ATOMS, THE FOAM HAVING
 1. A WATER ABSORBING CAPACITY OF AT LEAST ABOUT 700 PERCENT BY WEIGHT.
 2. A DENSITY OF AT LEAST 8 POUNDS PER CUBIC FOOT (125 KG/M3).
 2. A density of at least 8 pounds per cubic foot (125 kg/m3).
 2. A unitary article according to claim 1 wherein the fibrous assembly portion is a needle punched non-woven web.
 3. A unitary article according to claim 2 wherein the foam and fibrous assembly portions are joined by needle punching.
 3. A volume change upon absorption of water of less than 0.4 percent per weight percent of absorbed water.
 3. A VOLUME CHANGE UPON ABSORPTION OF WATER OF LESS THAN 0.4 PERCENT PER WEIGHT PERCENT OF ABSORBED WATER.
 4. A 24 HOUR COMPRESSION SET OF LESS THAN 75 PERCENT.
 4. A 24 hour compression set of less than 75 percent.
 5. A bound water pickup of at least about 100 percent by weight, and, integrally joined thereto, a fibrous assembly portion.
 5. A BOUND WATER PICKUP OF AT LEAST ABOUT 100 PERCENT BY WEIGHT, AND, INTEGRALLY JOINED THERETO, A FIBROUS ASSEMBLY PORTION. 